The present invention relates to a self-adjustable pitch propeller for marine vessels.
A propeller is designed by taking many parameters into account in order to provide the optimum thrust to the marine vessel provided therewith. For example, design parameters such as dimensions of the marine vessel body, load of the marine vessel, engine power, density of the water the marine vessel cruises on are important inputs for determining the diameter and pitch of the propeller to be produced. Once a propeller designed with the blades thereof being static relative to the hub thereof has been produced, the propeller may become heavy in torque against the cruise conditions if the pitch thereof is large and it requires more power from the engine. However, if the pitch is low, i.e. if it is ‘light’, it cannot deliver enough engine power as thrust. In either case, performance of the propeller falls. Such a propeller designed with the blades thereof being static relative to its hub (not adjustable pitch) is known as the ‘fixed pitch propeller’.
Modification attempts against the lightness of the propeller do not work and a new propeller needs to be used. In the case where the propeller is heavy as term, the diameter can be downsized, however this brings along a number of problems (e.g. mass balancing problem of the propeller can take place due to the centrifugal force exerted, it cannot be possible for each blade to uniformly face water). Nevertheless such modification does not mean obtaining a propeller providing high performance in changing cruise condition, because when the conditions of the marine vessel changes, when the load thereof increases for instance, the performance of fixed pitch propeller falls again. For this reason, variable pitch type propellers have been proposed. Use of variable pitch propellers against variable conditions such as marine vessel speed and load improves the performance (and therefore reduces fuel consumption). On the other hand, blades of the variable pitch propellers are rotated by a certain amount relative to the blade hub so as to provide the optimum pitch by being controlled according to each changing condition. This often requires using a complex and costly control/drive mechanism.
Typically, the pitch of a propeller is calculated according to shaft torque at which the motor that the propeller attached to is in its maximum speed (rpm). However, it is known that there is a considerable torque (and so power) difference between the shaft and propeller when the motor is run at moderate and lower speeds for maintaining fuel consumption lesser. At moderate and lower motor speeds, propellers produce less torque and therefore propellers should have a higher pitch to be economic in terms of fuel consumption and to increase cruise speed at such motor speeds. There seems to be no affordable and straightforward solution for self-adjusting the pitch of a propeller according to the motor speed.
Therefore, a propeller providing optimum thrust to a marine vessel according to the changed cruise conditions such as load and speed by adjusting the pitch in a simple and inexpensive way is needed.